How to develope and add new user functions to php

Hi all, I am PHP develope newbie. I now meet a problem. What I want is, when someone call my function, it will get the toppest caller's name/path and check its MD5SUM and create time, if they are legal, I will return the the secret data they want. For example, someone visit the url: http://mydomain.com/test.php in test.php, include ("func.inc") in func.inc, call_user_function load_name <== this is the function I want this function will check the md5sum and create time of the script test.php, if they match the condition, it will return the "value" according to the parameter "name" I think this function should not be a script. Because if it is script, any hacker can remove the authtication in this function and call the decrypt function to get my secret data directly. So in this case, if a hacker intrudes my website, he can change anything, but he can't get something like database passwords. This is exactly what I want. Actually I never develped any php lib or extention before. Can anybody give me a suggestion? I really don't know how to do that. I just know what I want. Here is my question: Is there any easy way to do that? e.g. call an external program. But how to pass the top caller's name to the external program? How to develpe and add a lib or extension or user function to php. I want to make things easy. The idea case is, I don't need to change my current php, just add the new module to the current php. How to get the top caller's name in a extension or lib or user function. (I use language C) Allen Zhao